By Dr. Artemis P. Simopoulos

Over the past 20 years many studies and clinical investigations have been carried out on the metabolism of polyunsaturated fats in general and on omega-3 fats in particular.

Today we know that omega-3 fats are essential for normal growth and development and may play an important role in the prevention and treatment of coronary artery disease, hypertension, diabetes, arthritis, other inflammatory and autoimmune disorders, and cancer (1-7).

Research has been done in animal models, tissue cultures, and human beings. The original observational studies have given way to controlled clinical trials. Great progress has taken place in our knowledge of the physiologic and molecular mechanisms of the various fats in health and disease. Specifically, their beneficial effects have been shown in the prevention and management of:

• Coronary heart disease (8, 9),
• Hypertension (10-12)
• Type 2 diabetes (13, 14)
• Renal disease (15, 16)
  
• Rheumatoid arthritis (17)
• Ulcerative colitis (18)
• Crohn disease (19)
• Chronic obstructive pulmonary disease (20)
  

However, this review focuses on the evolutionary aspects of diet, the biological effects of omega-6 and omega-3 fats, and the effects of dietary -linolenic acid (ALA) compared with long-chain omega-3 derivatives on coronary heart disease and diabetes.

Essential Fats Such As Omega-6 And Omega-3 Have Been Part Of Our Diet Since The Beginning Of Human Life

Before the agricultural revolution 10,000 years ago humans consumed about equal amounts of both. Over the past 150 years this balance has been upset. Current estimates in Western cultures suggest a ratio of omega-6 to omega-3 fats of 10-20:1 instead of 1-4:1.

On the basis of estimates from studies in Paleolithic nutrition and modern-day hunter-gatherer populations, it appears that human beings evolved consuming a diet that was much lower in saturated fats than is today's diet (21).

Furthermore, the diet contained small and roughly equal amounts of omega-6 and omega-3 PUFAs (ratio of 1-2:1) and much lower amounts of trans fats than does today's diet (21, 22). The current Western diet is very high in omega-6 fats (the ratio of omega-6 to omega-3 fats is 20-30:1) because of the indiscriminate recommendation to substitute omega-6 fats for saturated fats to lower serum cholesterol concentrations (23).

Intake of omega-3 fats is much lower today because of the decrease in fish consumption and the industrial production of animal feeds rich in grains containing omega-3 fats, leading to production of meat rich in omega-6 and poor in omega-3 fats (24). The same is true for cultured fish (25) and eggs (26).

Even cultivated vegetables contain fewer omega-3 fats than do plants in the wild (27, 28). In summary, modern agriculture, with its emphasis on production, has decreased the omega-3 fat content in many foods: green leafy vegetables, animal meats, eggs, and even fish.

Biological Effects of Omega-6 and Omega-3 Fats

Linoleic acid and alpha linolenic acid ALA and their long-chain derivatives are important components of animal and plant cell membranes. When you eat fish or fish oil, the EPA and DHA partially replace the omega-6 fats especially arachidonic acid in cell membranes.

As a result eating EPA and DHA from fish or fish oil leads to:

1) Decreased concentrations of thromboxane A2, a potent platelet aggregator and vasoconstrictor;

2) Decreased formation of leukotriene B4, an inducer of inflammation and a powerful inducer of leukocyte chemotaxis and adherence;

3) Increased concentrations of thromboxane A3, a weak platelet aggregator and vasoconstrictor;

4) Increased concentrations of prostacyclin PGI3, leading to an overall increase in total prostacyclin by increasing PGI3 without decreasing PGI2 (both PGI2 and PGI3 are active vasodilators and inhibitors of platelet aggregation); and

6) Increased concentrations of leukotriene B5, a weak inducer of inflammation and chemotactic agent (29, 30).

Because of the increased amounts of omega-6 fats in the Western diet, the eicosanoid metabolic products from arachadonic acid, specifically prostaglandins, thromboxanes, leukotrienes, hydroxy fats, and lipoxins, are formed in larger quantities than those formed from omega-3 fats, specifically EPA.

A diet rich in omega-6 fats shifts the physiologic state to one that is prothrombotic and proaggregatory, with increases in blood viscosity, vasospasm, and vasoconstriction and decreases in bleeding time.

The higher the ratio of omega-6 to omega-3 fats the higher is the death rate from cardiovascular disease (33). As the ratio of omega-6 to omega-3 increases, the prevalence of type 2 diabetes also increases (13).

Effects of Dietary Flax Compared With Fish Oil

ALA, found in flax seed is the precursor of omega-3 fats, can be converted to long-chain omega-3 fats and can therefore be substituted for fish oils.

However, ALA is not equivalent in its biological effects to the long-chain omega-3 fats found in marine oils. EPA and DHA are more rapidly incorporated into plasma and membrane lipids and produce more rapid effects than does ALA.

Experimental studies suggest that intake of 3-4 grams of ALA per day is equivalent to 0.3 grams (300 mg) EPA per day.

Relatively large reserves of LA in body fat, as are found in vegans or in the diet of omnivores in Western societies, would tend to slow down the formation of long-chain omega-3 fats like EPA and DHA from ALA.

One advantage of the consumption of ALA over omega-3 fats from fish is that the problem of insufficient vitamin E intake does not exist with high intake of ALA from plant sources.

Benefits of Omega-3 Fats

Dietary intake of omega-3 fats from seafood was associated with reduced risk of primary cardiac arrest compared with no fish intake; 5.5 g omega-3 fats per month or the equivalent of 1 fatty fish meal per week was associated with a 50% reduction in the risk of primary cardiac arrest.

A 5.0% increase in omega-3 fats was associated with a 70% reduction in the risk of primary cardiac arrest.

An increase in EPA and DHA also leads to increases in membrane fluidity, the number of insulin receptors, and insulin action.

Clinical interventions provide further support for the beneficial effects of omega-3 fats in the prevention and management of cardiovascular disease, hyperinsulinemia, and possibly type 2 diabetes.

Omega-3 fats affect coronary heart disease beneficially not by changing serum lipid concentrations, although EPA and DHA do lower triglycerides, by reducing blood clotting in vessel walls (72, 76) and ventricular arrhythmias (8, 9, 75, 77).

Am. J. Clinical Nutrition, September 1999; 70: 560 - 569

References

Dr. Mercola's Comments:

Always remember omega-3 fats are essential to your, and your children's, health. The best source for omega-3 is fish oil and cod liver oil, as, unlike other sources such as walnuts or flax seeds, it is high in two fatty acids crucial to human health, DHA and EPA. These two fatty acids are pivotal in preventing heart disease, cancer, and many other diseases. The human brain is also highly dependent on DHA - low DHA levels have been linked to depression, schizophrenia, memory loss, and a higher risk of developing Alzheimer's. When choosing your fish oil or cod liver oil, it is important to remember that not all brands are the same. In my research -- and in my clinical experience with my patients -- I have found that 1) the liquid form is superior to capsules; 2) that certain brands definitely seem inferior to others; 3) that the Carlson's brand of fish oil/cod liver oil is of an exceptional quality and purity. It is likely not the only brand in the world of such high quality, but up to this point it is the only one of such quality that I can recommend, so I now offer the Carlson's fish oil and cod liver oil on Mercola.com; you can also check your local health food store to see if they carry it. As for fish itself, patients consuming nearly every type of fish these days are showing high levels of mercury in their systems. In short -- and sadly, as it would otherwise be one of the healthiest meats on the planet -- I now advise against consuming any fish from any source, including fresh water, farm-raised or ocean, because most are contaminated with mercury. If you do consume fish, you should be certain the provider can demonstrate that the fish are free of detectable levels of mercury and other toxins (Carlson's fish oil/cod liver oil has been entirely purified so you don't have to worry about these toxins.) So what is the difference between fish oil and cod liver oil? In short, fish oil should be consumed in warm weather months and warm climates, while cod liver oil should be consumed in cool weather months and cool climates. Cod liver oil is high in vitamin D (and vitamin A); those in cool weather climates do not generally get enough vitamin D. However, in warm weather, their vitamin D is usually sufficient, as sunshine is one of the primary methods of obtaining this vitamin; if you consume too much vitamin D in these warm weather months, you do risk overdosing. A reasonable dose for both fish oil and cod liver oil is one teaspoon for every 50 pounds of body weight daily. Generally, our diets contain not only far too little omega-3, but far too many omega-6 fats. Experts looking at the dietary ratio of omega-6 to omega-3 fatty acids suggest that in early human history the ratio was about 1:1. Currently most Americans eat a dietary ratio that falls between 20:1 and 50:1. The optimal ratio is most likely closer to the original ratio of 1:1. For most of us this means not only increasing our omega-3 intake through fish oil, but also greatly reducing the omega-6 fatty acids we consume. Please recognize that we get ALL the omega-6 (and omega-9) fat we need from food. We do NOT need to take any supplements for these fats. Many of the omega fat supplements you see in health food stores will only serve to worsen your health, not improve it, as they contain omega-6 fats that will only worsen your omega-6 to omega-3 ratio. I strongly recommend avoiding sunflower, corn, soy, safflower, and canola oil, and products that contain these oils. This also means no hydrogenated or partially hydrogenated fats, no margarine, no vegetable oil and no shortening. These oils are full of omega-6 fats and will only worsen your omega-6 to omega-3 ratio. Acceptable oils include high-quality extra virgin olive oil, coconut oil, avocados and organic butter... or better yet, grass-fed organic butter. Another way to improve your omega 6:3 ratio is to change the type of meat you are eating. Since I can't recommend fish due to their high levels of mercury and other toxins these days, the best meats are those raised primarily or entirely on grass diets. Nearly all cattle found in grocery stores and restaurants are grain-fed before slaughter, so if you eat this type of beef, it will typically worsen you omega 6:omega 3 ratio. Though it may sound unusual to some, two of the best meats on the planet -- in terms of nutrition value and their incredible taste -- are bison and ostrich. And on Mercola.com, I offer bison meat and our exclusive omega-3-rich ostrich meat, both of which are free-ranged, fed primarily grass/alfalfa diets, and contain no antibiotics or steroids. Whether from my site or elsewhere, I urge you to try bison and ostrich. You can also consume a more "gamey" meat like venison, or try grass-fed beef, which I also highly recommend on Mercola.com. The grass-fed beef I recommend is even higher in omega-3 than fish, with a 6:3 ratio of 0.16 to 1 (this information is from a study done at Iowa State University in August 2001). It is still hard to find in grocery stores, however, and unlike bison and ostrich -- which both taste like prime beef -- some find the taste of grass-fed beef too lean. On a side-note, you should be cautious of stores advertising grass-fed beef that really isn't true grass-fed. ALL cattle are grass-fed to some small extent, but the key is what they are fed the months prior to being processed. Most all cattle are shipped to giant feed lots and fed corn to fatten them up. Your best bet is to call the person who actually grew the beef, NOT the store manager, to find out the truth. Another effective way to determine if the meat is really from a grass-fed animal is to purchase the ground beef and slowly cook it until it's done, then drain and collect all the fat. Grass-fed beef will contain a relatively small amount of such fat compared to traditionally prepared ground beef (which is why some find the taste of grass-fed too lean!) In summary: 1) Most Americans, young and old, are highly deficient in omega-3, and one of the best things you can do for yourself and your children is routinely consume fish oil in warm months and cod liver oil in cool months, as they are high in the best kind of omega-3. 2) You should cut out or reduce the oils and foods high in omega-6 fats, as Americans get far too much of them. This includes corn, sunflower, soy, canola and safflower oil, margarine, vegetable oil and shortening. 3) You should eat healthy meats, as store-bought beef and other common meats can worsen your omega-6 to omega-3 ratio. Bison and ostrich are two great-tasting and very healthy choices, and game animals or beef that is truly grass-fed are other good options.